1. Field of the Invention
The present invention generally relates to the separation and disposal of an undesired heavier fluid, such as water, from a desired lighter fluid, such as oil and gas, below ground surface in a production well and, more particularly, is concerned with a formation injection tool for down-bore in-situ disposal of the undesired heavier fluid in the production well.
2. Description of the Prior Art
Oil and/or gas subterranean wells often pass downward through productive formations whose yield, besides a desired lighter fluid, such as oil and/or gas, also includes an undesired heavier fluid, such as water (including salt water). Thus, relatively large quantities of undesired fluid are frequently produced along with the desired fluid. This is particularly true during the latter stages of the productive life of a well. Handling and disposing of the undesired fluid represents a significant expense in the production of desired fluid from these latter-stage wells.
Two basic approaches have been proposed and employed for separation of desired fluid from the undesired fluid and for disposal of the undesired fluid. The first approach, which for the sake of brevity is hereinafter called the "surface" approach, has seen widespread use. The second approach, which for the sake of brevity is hereinafter called the "in-situ" approach, has seen limited use, if any.
The surface approach involves pumping both desired and undesired fluids to above ground surface where they are then separated using various techniques. The separated undesired fluid is then disposed of by first transporting them to and then pumping them downward through a separate costly disposal well and into a subterranean disposal formation. In many cases, especially in latter-stage wells, the surface approach has proven to be too costly to economically produce the desired fluid from these wells, resulting in plugging of the wells and loss of potential revenues and reserves therefrom. Also, pumping the undesired fluid to the ground surfaces raises the potential for adverse environmental impacts during transport and disposal.
The in-situ approach involves separating the undesired fluid from the desired fluid, usually by gravity, in the production well below ground surface. Thus, only the desired fluid is raised to the ground surface, the undesired fluid being separately conveyed downwardly through the well bore and discharged into a disposal formation below the productive formation without first raising the undesired fluid to the ground surface. The in-situ approach has potential advantages and benefits over the surface approach in terms of lower cost and less adverse environmental impacts.
Representative of the production apparatus taking the in-situ approach are the ones disclosed in U.S. patents to Niles (U.S. Pat. No. 2,214,064), Barr (U.S. Pat. No. 2,988,215), Bryan (U.S. Pat. No. 3,167,125), Jacob (U.S. Pat. Nos. 3,195,633 and 3,199,592), Bishop (U.S. Pat. Nos. 3,333,638 and 3,363,692), Price (U.S. Pat. Nos. 4,241,787 and 4,296,810) and McIntyre (U.S. Pat. No. 4,766,957).
U.S. Pat. No. 2,214,064 to Niles discloses a production apparatus located above a packer in a well casing being perforated both above and below the packer. The Niles apparatus includes a lower pump located above the packer, a separator located above the lower pump, and an upper pump located above the separator. The lower pump receives both oil and water from a porous formation above the packer and conveys the oil and water into the separator. The separator causes separation of the oil from the water, conveying the oil upwardly to the upper pump and the water downwardly through the packer, by-passing the lower pump, and into the porous formation below the packer. The upper pump conveys the separated oil from the well.
U.S. Pat. No. 2,986,215 to Barr discloses a salt water disposal apparatus which includes a production standpipe located in a well casing. The standpipe has an outer tube portion being mounted by a pair of spaced upper and lower packers so as to extend below, between and above the packers. The standpipe also has an inner tube portion connected at a lower end to a side of the outer tube for receiving a mixture of water and oil or gas from a formation between the spaced packers and routing the mixture to above the upper packer where the lighter oil or gas rises in the well while the heavier water descends and flows through apertures in the outer tube and then downwardly through the outer tube to a disposal formation located below the lower packer.
U.S. Pat. No. 3,167,125 to Bryan discloses a reciprocal tubular pump disposed in a well casing with its upper end secured to the lower end of a tubing string and its lower end secured to a packer in the well casing. The pump draws in a mixture of oil and water from an annulus between the casing and pump which communicates with the productive formation. The mixture is pumped upwardly to above the pump where the heavier water separates from the lighter oil and flows downwardly through an internal passage within the pump body and through the packer to a disposal formation below the packer.
U.S. Pat. Nos. 3,195,633 and 3,199,592 to Jacob disclose apparatuses for separating and producing oil from water in a well which employs a pair of spaced lower and upper packers and a pair of upper and lower pumps disposed in the well with the lower pump being disposed between the packers and the upper pump being disposed above the upper packer. The upper pump receives lighter oil from a production formation above the upper packer and pumps the lighter oil upwardly to the surface whereas the lower pump receives the heavier water from the formation between the spaced packers and pumps the heavier water downwardly through the lower packer to a disposal formation.
U.S. Pat. Nos. 3,333,638 and 3,363,692 to Bishop disclose apparatuses for disposing of water into a disposal formation located below a production formation by producing a head of water in a tube string above a packer and then, either due to hydrostatic pressure of the head of water or due to a vacuum created below a lower restriction, by forcing or pulling the water downwardly through the packer and into the lower disposal formation.
U.S. Pat. Nos. 4,241,787 and 4,296,810 to Price disclose downhole separator assemblies for separation of oil and water which employ a filter member with membrane sheets operative to separate the oil and water and wherein separated water is then conveyed downwardly through the wellbore and discharged into a disposal formation at a lower elevation below a packer without first raising the water with the oil to the surface.
U.S. Pat. No. 4,766,957 to McIntyre discloses an apparatus for effecting gravitational separation of hydrocarbons and water discharged from a production formation of a subterranean well. The well casing extends downwardly beyond a production zone to a water absorbing zone of the well. A mixture of hydrocarbons and water flows into the interior of the casing through perforations disposed adjacent the production zone. A fluid collection chamber is provided either exteriorly or interiorly of the casing perforations permitting the hydrocarbons to rise to the top of any water. The water flows downwardly, or is forcibly pumped downwardly to the water absorbing formation. The water enters the lower inlet end of the pump and discharges from an upper outlet end thereof. The water discharged by the pump then flows downwardly through a bypass conduit extending downwardly past the exterior of the pump to an inlet to the lower packer where the water then flows through the packer and to the lower water absorbing zone of the well.
While the apparatus of the above-described patents represent a step in the right direction in adopting the in-situ approach of separation and disposal of undesired fluids in the production well, they appear to embody drawbacks in terms of complexity, high cost and serviceability which makes each of them much less than an optimum solution to the problem of cost-effective disposal of undesired fluids. Consequently, a need still exists for an in-situ disposal method which will overcome the drawbacks of the prior art without introducing new ones in their place.